Reduction of RF Electrode Edge Effect

ABSTRACT

A skin surface is treated with RF energy (e.g., unipolar, monopolar, bipolar or multipolar RF delivery). A first semiconductive cap disposed on a first distal end of a first electrode and, optionally, a second semiconductive cap disposed on a second distal end of a second electrode are applied to the skin surface. RF energy is delivered from the first electrode and the second electrode through the first semiconductive cap and the second semiconductive cap, respectively, through the skin surface. The first semiconductive cap and/or the second semiconductive cap have an electrical conductivity matched or substantially matched to the skin&#39;s electrical conductivity (e.g., about 0.1 to about 2 times that of the skin).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/402,320 filed Feb. 22, 2012, the entire disclosure of whichis herein incorporated by reference.

FIELD

The invention relates generally to radio frequency (RF) energy treatmentdevices, and more particularly, to improving the delivery of RFelectrical energy to tissue by reducing edge effects and improving thespatial uniformity of energy delivered to skin or other tissues.

BACKGROUND

Many aesthetic dermatologic procedures resort to delivering thermalenergy to skin or underlying subcutaneous tissue as a means to stimulatea therapeutic effect. Procedures such as skin resurfacing, skintightening, wrinkle reduction, hair reduction, tattoo removal, bodycontouring, and treatments for excessive sweating, sebaceous glandproduction, acne, pigmented lesions, vascular lesions and blood vesselstake advantage of heat to achieve a desired effect. Many differenttechnologies can be used to heat the skin and/or underlying tissuesincluding lasers, incoherent light sources, radiofrequency electricalenergy sources, and ultrasound energy sources.

A problem with delivering RF energy to tissue is the fundamentalconcentration of current density along the edges of the electrode incontact with tissue. For monopolar RF energy delivery, higher skinsurface temperatures occur along the entire perimeter of the electrode.For bipolar RF energy delivery, the concentration of current also occursalong the edges, but even higher current densities occur along the innertwo edges forming the gap between the two electrodes having the shortestelectrical path. These non-uniform thermal effects limit the amount ofenergy that can be delivered to tissue so as to avoid adverse skineffects such as burns, blisters, and erythema.

SUMMARY

The invention, in various embodiments, features a method and apparatusthat uses a semiconductive material applied to an electrode thatoptimizes electrical energy delivered to tissue while minimizing thermalhotspots around edge of the electrode. The semiconductive material neednot be specific to semiconductors typically used in electroniccomponents (e.g., silicon, germanium, gallium arsenide, etc.), but canrefer more generally to any material whose conductivity lies betweenconductors and insulators (typically between 103 to 10-8 S/m).

The semiconductive material can be a ceramic material. Thesemiconductive material can have a specified electrical conductivity toimprove the spatial uniformity of energy delivered to skin or othertissues and a specified thermal conductivity so that heat at the metalelectrode-ceramic junction is carried away via a heat sink and does notaccumulate causing unwanted skin surface heating. The semiconductivematerial can have an electrical conductivity matched or substantiallymatched to the skin's electrical conductivity (e.g., about 0.1 to about2 times that of the skin). In addition, the ceramic can have a lowcoefficient of thermal expansion and be relatively scratch resistant.The semiconductive material can have an electrical conductivity of about0.03 S/m to about 3.0 S/m (e.g., about 0.03 S/m to about 0.3 S/m) and athermal conductivity of about 5 W/m·° C. to about 500 W/m·° C.

The semiconductive material can be a cap on the electrode, and can havea geometric shape that facilitates relocation of hotspots to reduce oreliminate thermal damage by the electrode. The semiconductive materialcan be graded to be thicker at the edges of the electrode than in thecenter. In certain embodiments (e.g., unipolar, monopolar, bipolar ormultipolar RF delivery), the cap can have a trapezoidal verticalcross-section so that the thermal hot spot occurs inside the cap. Invarious embodiments, the ceramic can be axially asymmetric so that it isthicker along its inner edge compared to its outer edge. The inner edgeis the edge adjacent to the next closest electrode. For unipolar andmonopolar RF applicators, the electrode cap can be axially symmetricwhereas for bipolar and multipolar RF applicators the electrode cap canbe axially symmetric or axially asymmetric.

In one aspect, there is an applicator for RF energy delivered through askin surface. The applicator includes a base, a first electrodeconnected to the base, and a first semiconductive cap disposed on afirst distal end of the first electrode. The first electrode extendsfrom the base toward a first location of the skin surface. The firstsemiconductive cap is configured to contact the first location of theskin surface. The RF energy is delivered from the first electrodethrough the first semiconductive cap through the skin surface. Incertain embodiments, the applicator includes a second electrodeconnected to the base and a second semiconductive cap disposed on asecond distal end of the second electrode. The second electrode extendsfrom the base toward a second location of the skin surface. The secondelectrode is laterally offset from the first electrode along the skinsurface. The second semiconductive cap is configured to contact thesecond location of the skin surface. The RF energy is delivered from thefirst electrode and the second electrode through the firstsemiconductive cap and the second semiconductive cap, respectively,through the skin surface. The RF energy delivered by the first electrodecan have opposite phase to the RF energy delivered by the secondelectrode.

In another aspect, there is an apparatus of treating a skin surface withRF energy. The apparatus includes applying to the skin surface a firstsemiconductive cap disposed on a first distal end of a first electrodeand delivering RF energy from the first electrode through the firstsemiconductive cap through the skin surface. In some embodiments, theapparatus includes applying to the skin surface a second semiconductivecap disposed on a second distal end of a second electrode and deliveringRF energy from the first electrode and the second electrode through thefirst semiconductive cap and the second semiconductive cap,respectively, through the skin surface.

In still another aspect, there is an apparatus for treating a skinsurface with RF energy. The apparatus include means for applying to theskin surface a first semiconductive cap disposed on a first distal endof a first electrode and means for delivering RF energy from the firstelectrode through the first semiconductive cap through the skin surface.In some embodiments, the apparatus includes means for applying to theskin surface a second semiconductive cap disposed on a second distal endof a second electrode and means for delivering RF energy from the firstelectrode and the second electrode through the first semiconductive capand the second semiconductive cap, respectively, through the skinsurface.

In other examples, any of the aspects above, or any apparatus, system ordevice, or method, process or technique, described herein, can includeone or more of the following features.

In various embodiments, the source provides monopolar RF energy orbipolar RF energy. The RF energy can have a frequency of about 100 kHzto about 10 MHz (e.g., about 1 MHz). The source can provide the RFenergy at about 10 J/cm3 to about 500 J/cm3 (e.g., about 50 J/cm3 toabout 120 J/cm3). The source can provide the RF energy in pulses ofabout 0.1 second to about 1 second.

In various embodiments, the electrical conductivity of eachsemiconductive cap is matched or substantially matched to theconductivity of the skin (e.g., 0.1 to about 2 times that of skin at thefrequency of interest). The electrical conductivity of eachsemiconductive cap can be matched so that about 5% to about 30% (e.g.,about 10%) of the RF energy is lost to the semiconductive cap. The firstsemiconductive cap and/or the second semiconductive cap can have anelectrical conductivity of about 0.03 S/m to about 3.0 S/m (e.g., 0.11S/m). The thermal conductivity can be about 5 W/m·° C. to about 500W/m·° C. or about 50 W/m·° C. to about 250 W/m·° C.

In certain embodiments, the first semiconductive cap and/or the secondsemiconductive cap has/have a trapezoidal vertical cross-sectionincluding a first surface and a second surface parallel or substantiallyparallel to the first surface. The first surface adjoins the firstelectrode, and the second surface is configured to contact the firstlocation of the skin surface. The trapezoidal vertical cross-section canbe an isosceles trapezoidal vertical cross-section. A cap can include athird surface forming an obtuse angle with the first surface so that thesecond surface is longer than the first surface.

In various embodiments, each semiconductive cap tapers from an inneredge to the center. The thickness of each semiconductive cap between theblunt surface and the curved surface can be thickest at the innerportion, thinnest at the center portion, and thicker than the centerportion but thinner than the inner portion at an outer portion.

In various embodiments, each semiconductive cap tapers from an inneredge to the center. The thickness of each semiconductive cap between theblunt surface and the curved surface can be thickest at the innerportion and thinner at the center portion and outer portion.

In various embodiments, each semiconductive cap can extend along theskin surface beyond the electrode such that the extension tapers towardsthe inner edge.

In various embodiments, each semiconductive cap includes asemiconductive ceramic. Each semiconductive cap can include a conductivesilicon carbide based ceramic doped with a nonconductive material and/ora nonconductive aluminum nitride based ceramic doped with a conductivematerial. In certain embodiments, each semiconductive cap is affixed tothe respective electrode with a conductive epoxy. In certainembodiments, each semiconductive cap is metalized so that thesemiconductive cap can be soldered or brazed to the electrode.

In certain embodiments, the applicator can include a waveguide disposedbetween the first electrode and the second electrode to deliver opticalradiation. The third surface of a semiconductive cap can abut a surfaceof the waveguide. The applicator can include one or more electricallyinsulating regions having a triangular vertical cross section disposedbetween a surface of the waveguide and one of the semiconductive caps.

Other aspects and advantages of the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings, illustrating the principles of the invention byway of example only.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of the invention described above, together with furtheradvantages, may be better understood by referring to the followingdescription taken in conjunction with the accompanying drawings. Thedrawings are not necessarily to scale, emphasis instead generally beingplaced upon illustrating the principles of the invention.

FIG. 1 shows a cross-section of a temperature profile in skin for amonopolar copper electrode applied to a skin surface without asemiconductive cap.

FIG. 2 shows a cross-section of a temperature profile in skin forbipolar copper electrodes applied to a skin surface withoutsemiconductive caps.

FIG. 3 shows a cross-section of a temperature profile in skin when usingsemiconductive caps on the electrodes.

FIG. 4 shows a cross-section of a temperature profile in skin when usingsemiconductive caps having a variable thickness.

FIG. 5 shows a cross-section of another temperature profile in skin whenusing semiconductive caps with a variable thickness.

FIG. 6 shows a cross-section of another temperature profile in skin whenusing semiconductive caps having a trapezoidal cross-section.

FIG. 7A shows a sectional view of an applicator for RF energy deliveredthrough a skin surface.

FIG. 7B shows a sectional view of a semiconductive cap for an electrode.

FIG. 7C shows a side elevation view of a semiconductive cap for anelectrode.

FIG. 8A shows a perspective view of another electrode and semiconductivecap embodiment.

FIG. 8B shows a side view of the embodiment shown in FIG. 7A.

FIG. 9A shows a cross-section of a temperature profile in skin whenusing semiconductive caps having an elliptical shape.

FIG. 9B shows temperature of the skin between electrodes.

FIG. 10 shows RF power absorption for an electrode including arectangular shaped cap.

FIG. 11 shows RF power absorption for an electrode including atrapezoidal shaped cap.

FIG. 12 shows a vertical cross-section of an applicator for RF energy.

FIG. 13 shows an exploded view of a semiconductive cap.

FIG. 14 a vertical cross-section of another applicator for RF energy.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 shows a cross-section of a temperature profile in skin for amonopolar copper electrode applied to a skin surface without asemiconductive cap. FIG. 2 shows a cross-section of a temperatureprofile in skin for bipolar copper electrodes applied to a skin surfacewithout semiconductive caps. Uneven heat distribution is seen at theedges of the monopolar electrode and is symmetric (equal at both edges).For the bipolar electrodes, the uneven heat distribution is seen at theedges, but is asymmetric. The current density is greater along the innerelectrode edges because the path length is shorter and hence impedanceis lower. More current will travel this path. In both examples, 20joules of RF energy is delivered to tissue. In general, temperaturesgreater than 70° C. lead to adverse skin effects such as blisters.

FIG. 3 shows a cross-section of a temperature profile in skin when usingsemiconductive caps (e.g., formed from a ceramic material) on theelectrodes. In the figure, the caps are illustrated, but the electrodesare not. The energy delivered to tissue is 20 joules, the same as wasused in FIG. 2, but because the impedance between the cap and the tissueis better matched, the thermal hotspot is smaller. The hotspots appearon the inner edges due to the shorter electrical path length to the nextadjacent electrode. High current densities also exist at the edge of thecopper electrode-ceramic cap junction. Because of the high thermalconductivity of ceramic, heat at this junction is effectively conductedtowards the electrode, so this density does not cause thermal hotspotsat this junction and prevents overheating on the cap which is in contactwith the skin.

FIG. 4 shows a cross-section of a temperature profile in skin when usingsemiconductive caps with a variable thickness. In the figure, the capsare illustrated, but the electrodes are not. Because ceramic has finiteimpedance, it can be shaped to be thicker at the edges to furtherminimize the thermal hotspot on the inner edges causes by the shorterelectrical pathlength. In this case, two times more energy or 40 Joulesis delivered to skin, but the thermal hotspots are about half what isseen without the ceramic cap and more importantly less than the 70° C.critical temperature. In this case, the temperature of skin (1 mm deep,halfway between electrodes) is increased to about 42.8° C., an increaseof about 10.8 degrees over the starting temperature of about 32° C.Without the ceramic cap, the increase is about 36.2° C. or only about4.2 degrees above the initial temperature. So with the cap, the skin ismore effectively heated with less risk of adverse effects to the skinsurface underneath the electrodes.

FIG. 5 shows a cross-section of a temperature profile in skin when usingsemiconductive caps with a variable thickness. In the figure, the capsare illustrated, but the electrodes are not. Each cap has a bluntsurface in contact with the skin and a curved surface contacting theelectrode. Each cap is asymmetric, being thickest at the inner portion,thinnest at the center portion, and thicker than the center portion butthinner than the inner portion at an outer portion. In the centerportion, the cap tapers from thicker than the outer portion to thinnerthan the outer portion. In this case, 48 Joules of RF energy isdelivered, but the thermal hotspots remain under 70° C. The temperatureof skin (1 mm deep, halfway between electrodes) is increased to about40° C. or an increase of about 8° C. Compared with the bare copperelectrode, the mid-dermal increase is two times higher while theelectrode hotspots are two times lower. In this configuration, a largervolume of tissue is heated compared to the previous configuration so thechange in temperature is not as high even through more energy is beingdelivered to tissue.

FIG. 6 shows a cross-section of a temperature profile in skin when usingtrapezoidal semiconductive caps. In the figure, the caps areillustrated, but the electrodes are not. Each cap has a first surfaceand a second surface parallel to the first surface wherein the firstsurface adjoins the first electrode and the second surface is configuredto contact the skin surface. In this case, 44 Joules of RF energy isdelivered, and the thermal hotspots remain under 70° C. The temperatureof skin (1 mm deep, halfway between electrodes) is increased to about39.6° C. or an increase of about 7.6° C. Compared with the bare copperelectrode, the mid-dermal increase is two times higher while theelectrode hotspots are two times lower. In this configuration, a largervolume of tissue is heated compared to the configuration used in FIG. 4so the change in temperature is not as high even through more energy isbeing delivered to tissue. Unlike the previous configurations, more RFenergy will be lost to the semiconductive caps. RF loss to the ceramiccaps is, in this case, about 30%. In FIGS. 5 and 6, the conductivity ofthe cap was about 0.11 S/m, about half that of skin.

FIG. 7A shows an applicator 10 for bipolar RF energy delivered through askin surface 14. The applicator 10 includes a base 18, a first electrode22 connected to the base 18, a second electrode 26 connected to the base18, a first semiconductive cap 30 disposed on a first distal end 34 ofthe first electrode 22, a second semiconductive cap 38 disposed on asecond distal 42 end of the second electrode 26. The first electrode 22extends from the base 18 toward a first location 46 of the skin surface14. The second electrode 26 extends from the base 18 toward a secondlocation 50 of the skin surface 14. The first electrode 22 is laterallyoffset along the skin surface 14 from the second electrode 26, and thecurrent through the first electrode 22 and the second electrode 26 haveopposite phases. Each electrode 22 or 26 can be cooled to about 10° C.using a thermoelectric cooler 52 attached to the side of the electrodeand or the base 18. Each electrode 22 or 26 can have separatethermoelectric coolers 52, which can be water or air cooled.

Base 18 can be any member to which the electrodes 22 and 26 areattachable. In some embodiments, base 18 is modular and includesseparate members for connection to electrodes 22 and 26. Base 18 can bea portion or section of a hand piece or applicator, or can be the handpiece or applicator. In some embodiments, base 18 and electrodes 22 and26 are integrally formed.

Each electrode 22 or 26 and/or each semiconductive cap 30 or 38 can havean elliptical shape so that first electrode 22 location 46 and secondelectrode 26 location 50 on the skin surface 14 sometimes termed asfootprints 46 and 50 of the caps 30 and 38 are elliptical or oval inshape. The treatment region 54 formed by the electrodes 22 and 26 and/orsemiconductive caps 30 and 38 can be rectangular in shape, and canextend into the skin surface to a predetermined depth.

FIG. 7B shows a sectional view of a semiconductive cap 30 (or 38) for anelectrode 22 (or 26). In one example, each electrode 22 (or 26) and eachsemiconductive cap 30 (or 38) is about 4 mm wide at axis 56 and 12 mmdeep at axis 57. Each electrode 22 or 26 can be about 4 to 15 mm long(e.g., about 12 mm long). The electrodes can be spaced apart by about 5to 20 mm (e.g., about 12 mm or about 13 mm from inner edge to inneredge).

Each electrode 22 or 26 can be an electrically conductive metal (e.g.,copper) or ceramic material. Each electrode 22 or 26 can be plated witha nonoxidizing surface such as chrome. Each electrode can be formed froma semiconductive ceramic with an appropriately shaped solder pad.

FIG. 7C shows a side elevation view through axis 56 of a semiconductivecap 30 (or 38) for an electrode 22 (or 26). The semiconductive cap 30(or 38) has a blunt surface 58 adapted to contact a location of the skinsurface 14 (e.g., the first location 46 if it is the firstsemiconductive cap 30 and the second location 50 if it is the secondsemiconductive cap 38). The semiconductive cap 30 (or 38) has a curvedsurface 60 that can be affixed to the first electrode 22 (or the secondelectrode 26). The thickness of each semiconductive cap 30 (or 38)between the blunt surface 58 and the curved surface 60 can be tapered orgraded from the inner edge to the outer edge. The semiconductive cap 30(or 38) can be thicker at an inner portion 62 and thinner at a centerportion 66 to homogenize the electrical field at the skin surface 14. Anouter portion 70 of the semiconductive cap 30 (or 38) can be thickerthan the center portion 66 but thinner than the inner portion 62. Inthis way, the entrance or exit point for current entering or leaving theelectrode is spread across the entire cap surface, which homogenizes thetissue entry current field. The inner edge or portion is theedge/portion adjacent to the next closest electrode.

In certain embodiments, along axis 56, the inner portion 62 is about 2mm thick, the center portion 66 is about 0.5 mm thick, and the outerportion 70 is about 1 mm. Along axis 57, the center is about 1 mm thickand the upper and lower edges are about 3 mm thick.

Referring back to FIG. 7A, a source 74 of RF energy is in electricalcommunication with the base 18 via cable 78, which can include a singlewire or a bundle of wires. Each electrode 22 and 26 includes a separatewire feed 80 and 84, respectively. Wire feeds 80 and 84 can be inelectrical communication with separate wires or feeds of cable 78.Source 74 can deliver RF energy to and through the skin surface 14. Thesource 74 can deliver RF energy via cable 78 to wire feed 80 and 84 tothe first electrode 22 and the second electrode 26, respectively. RFenergy can be delivered from the first electrode 22 and the secondelectrode 26 through the first semiconductive cap 30 and the secondsemiconductive cap 38, respectively, through the skin surface 14.

The electrical conductivity of the semiconductive material (e.g., theceramic material) can be approximate to the electrical conductivity ofskin at the tissue-electrode interface. In certain embodiments, theconductivity of each semiconductive cap can be matched or substantiallymatched to the conductivity of the skin. For example, the electricalconductivity of the cap can be about 0.1 to 2 times the skinconductivity. The conductivity of each semiconductive cap can be matchedso that about 5-30% (e.g., about 10%) of the RF energy is lost to thesemiconductive cap. The conductivity of each semiconductive cap can beabout 0.1 S/m at 1 MHz, which is about half of skin. The conductivity ofthe semiconductive caps can be graded such that the central and outerportions are more conductive than the inner portion.

If the electrical conductivity is exactly matched, then the current doesnot concentrate at the ceramic-tissue junction because, from anelectrical perspective, no junction exists because of the matchedconductivity values. The electrical conductivity for skin is about 0.22S/m at 1 MHz RF frequency. In this case, the hot spot occurs at themetal electrode-ceramic interface, which, because of the ceramic's highthermal conductivity, is quickly diffused so that little heating occursat the skin surface. However, RF energy is lost to the ceramic materialand the amount of energy lost is proportional to the electricalconductivity value. In the typical ceramic geometries used, the loss ofRF energy to ceramic can be as much as 50%. An electrical conductivityof 0.1 S/m at 1 MHz for the ceramic material can minimize this. Althoughnot exactly matched to skin, the amount of RF energy lost to the ceramicmaterial is around 10% while the thermal hotspot at the electrode edgeis greatly diminished compared to when the ceramic material is not used.

Each semiconductive cap can include a semiconductive ceramic, which canhave an electrical conductivity of about 0.03 S/m to about 3.0 S/m(e.g., about 0.05 S/m to about 0.3 S/m) and a thermal conductivity ofabout 5 W/m·° C. to about 500 W/m·° C. (e.g., about 50 to 250 W/m·° C.).The electrical conductivity can be about 0.1 S/m. The semiconductive capcan be a passive material in that material properties are independent oftemperature. The shape of the cap is made such that the electricalpathlength through the semiconductive cap or ceramic material towardsthe edges of the electrodes are longer than toward the center. Thispassively increases the resistance for current flowing towards the edgecompared to the center thereby better homogenizing the electric field atthe tissue surface. This effectively spreads the current density leavingthe probe over a larger area, which reduces the magnitude of the thermalhotspot.

Each semiconductive cap can include a conductive silicon carbide basedceramic doped with a nonconductive material and/or a nonconductivealuminum nitride based ceramic doped with a conductive material. Thenonconductive material or the conductive material can be used to tunethe cap to the desired conductivity.

A semiconductive cap can be formed by sintering silicon carbide. Theceramic can be prepared from a green preform, which can allow shaping ofthe electrode cap to the desired shape and can allow mixing of anadditional material to tune the electrical conductivity of the finishedproduct. Boron, aluminum and nitrogen are dopants that can be used tochange the electrical conductivity of silicon carbide materials. Incertain embodiments, the semiconductive cap is formed from AlN dopedwith TiB2.

Each semiconductive cap need not be permanently attached to anelectrode. Each semiconductive cap can be affixed, bonded or attached.Each semiconductive cap can be affixed to the respective electrode witha conductive epoxy. A silver conductive epoxy has good thermal andelectrical properties, and can bond to metals, glasses and ceramics.Each semiconductive cap can have one or more surfaces metalized withcopper, gold, silver or other materials so that the semiconductive capcan be soldered or brazed to the electrode.

Each semiconductive cap can be affixed to the respective electrode witha compressive tongue and groove joint. Each semiconductive cap can beaffixed to the respective electrode with a screw passing through the capand securing to the electrode. A compressive metal gasket can be used toimprove thermal and electrical conduction between the cap and theelectrode at the junction.

The source 74 can provide the RF energy at a frequency of about 100 kHzto about 10 MHz (e.g., about 1 MHz), although higher or lowerfrequencies can be used depending on the application. The source 74 caninclude a controller for the RF energy and/or a controller for thethermoelectric cooler 52. The source can provide the RF energy at about10 J/cm3 to about 500 J/cm3 (e.g., about 50 J/cm3 to about 120 J/cm3),although higher or lower fluences can be used depending on theapplication. Using a volumetric heat capacity of 4 J/cm3-oC for skin,120 J/cm3 corresponds to a 30° C. rise in skin temperature. The sourcecan provide the RF energy in pulses of about 0.1 second to about 1second, although shorter or longer durations can be used depending onthe application.

FIGS. 8A and 8B show a perspective view and a side view, respectively,of an electrode 22′ and semiconductive cap 30′, which can be used withbase 18 shown in FIG. 6A. Electrode 22′ can have a body portion 88, atip 92 and a flange 96. Tip 92 can extend about 3.5 mm from body 88, andcan be about 9 mm deep and 2 mm wide. Semiconductive cap 30′ can definean opening, which is insertable over tip 92. Semiconductive cap 30′ canabut flange 96 and be formed so that its outer surface is flush with theouter surface of the body portion 88 of the electrode 22′. Eachsemiconductive cap 30′ can be permanently or semi-permanently attachedto an electrode.

Cap 30′ can have a variable thickness, e.g., a thickness between theblunt surface and the curved surface is thicker at an inner portion andthinner at a center portion to homogenize the electrical field at theskin surface. The variable thickness of cap 30′ is symmetric. The cap30′ can be about 0.5 mm thick at the center and about 4.0 mm thickaround its perimeter. The cap 30′ can about 12 mm deep and 4 mm wide.The thickness of the wall surrounding the opening is about 1 mm in thex-plane and about 1.5 mm in the y-plane.

FIG. 9A shows a cross-section of a temperature profile in skin whenusing semiconductive caps with a variable thickness. In the figure, acap is illustrated, but the electrode is not. Each cap has a bluntsurface in contact with the skin and a curved surface contacting theelectrode. Each cap is elliptical or oval in shape. In this case, thehot zone around the edge is evenly distributed, with peak temperaturesreaching about 69° C. (e.g., thermal hotspots remaining under 70° C.).FIG. 9B shows temperature of the skin between electrodes, with thetemperature reaching a maximum about 2 mm from the electrode edge. Inthis configuration, a larger volume of tissue is heated compared to theprevious configurations so the change in temperature is not as high eventhrough more energy is being delivered to tissue.

FIG. 10 shows RF power absorption for an electrode 22″ including arectangular shaped cap 32, which has electrical conductivity matched toskin 14. While the hot spot 100 at the edge of the metal electrode isinside the cap, there is a hot spot 104 at the junction of the cap withthe skin. Current is forced to fold around this corner, creating a highconcentration there. Although much smaller than the hot spot without thesemiconductive cap, the hot spot can be further reduced as shown in FIG.11. The lines in FIG. 10 are power density contours in W/cm3.

FIG. 11 shows RF power absorption for an electrode 22″ including atrapezoidal shaped cap 30″. A triangular section 108 of trapezoidalshaped cap 30″ maintains the hot spot 100 inside the trapezoidal shapedcap 30″, but reduces or eliminates the hot spot 104 at the junction ofthe trapezoidal shaped cap 30″ with the skin 14. The trapezoidal shapedcap 30″ extends along the skin 14 surface beyond the electrode 22″ edge.The cap extension tapers down towards the inner edge of the electrode.

FIG. 12 shows another embodiment of an applicator 10″ for RF energy(monopolar or bipolar) delivered through a skin surface 14. Theapplicator 10″ includes a base 18″, a first electrode 22″ connected tothe base 18″, a second electrode 26″ connected to the base 18″, a firstsemiconductive cap 30″ disposed on a first distal end 34 of the firstelectrode 22″, a second semiconductive cap 38″ disposed on a seconddistal 42 end of the second electrode 26″. The first electrode 22″extends from the base 18″ toward a first location of the skin surface14. The second electrode 26″ extends from the base 18″ toward a secondlocation of the skin surface 14. The first electrode 22″ is laterallyoffset along the skin surface 14 from the second electrode 26″, and thefirst electrode 22″ and the second electrode 26″ have opposite phases.Each electrode 22″ or 26″ can be cooled to about 10° C. using athermoelectric cooler. Each cap extends along the skin surface beyondthe electrode edge. The cap extension tapers down towards the inner edgeof the electrode.

The applicator 10″ includes dielectric regions 112 and a waveguide 116for delivering optical radiation to the skin. The skin surface 14 isshown in FIG. 11 as the interface between air 120 and the skin 124comprising epidermal and dermal regions 128 and a subcutaneous fatregion 132. The waveguide 116 can be coupled to a source of opticalradiation, such as a laser or incoherent source.

In various embodiments, the optical source can produce radiation havinga wavelength between about 250 nm and about 2,600 nm, although longerand shorter wavelengths can be used depending on the application. Insome embodiments, the wavelength can be between about 400 nm and about1,800 nm. In some embodiments, the wavelength can be between about 400nm and about 1,100 nm. In some embodiments, the wavelength can bebetween about 1,160 nm and about 1,800 nm.

FIG. 13 shows an exploded view of a semiconductive cap 30″ or 38″. Thecap extends along the skin surface beyond the electrode edge. The capextension tapers down towards the inner edge of the electrode. The capcan have a trapezoidal vertical cross-section including a first surface136, a second surface 140 parallel or substantially parallel to thefirst surface 136, and a third surface 144 forming an obtuse angle Awith the first surface 136, and a fourth surface 148. The second surface140 is longer than the first surface 136. The second surface 140 isconfigured to contact the skin, and the first surface 136 is configuredto adjoin a respective electrode.

FIG. 14 shows another embodiment of an applicator 10′ for RF energydelivered through a skin surface (not shown). The applicator 10′includes a base 18″, a first electrode 22″ connected to the base 18″, asecond electrode 26″ connected to the base 18″, a first semiconductivecap 30′ disposed on a first distal end 34 of the first electrode 22″, asecond semiconductive cap 38′ disposed on a second distal 42 end of thesecond electrode 26″. The first electrode 22″ extends from the base 18″toward a first location 36 of the skin surface. The second electrode 26″extends from the base 18″ toward a second location 42 of the skinsurface. The first electrode 22″ is laterally offset along the skin 14surface from the second electrode 26″, and the first electrode 22″ andthe second electrode 26″ have opposite phases. Each electrode 22″ or 26″can be cooled to about 10° C. using a thermoelectric cooler.

The semiconductive caps 30′ and 38′ can be isosceles trapezoids or canhave a cross-section as defined in FIG. 12. The cap(s) can extend alongthe skin surface, but need not extend beyond the electrode edges. Eachcap extension can taper down towards either the inner or outer edge ofthe electrode, depending on the orientation of the extension.

The applicator 10′ includes a waveguide 116 for delivering opticalradiation to the skin and electrically insulating regions 152. Thewaveguide 116 can be coupled to a source of optical radiation, such as alaser or incoherent source. The waveguide 116 can have a straight edge,as opposed to the notched profile shown in FIG. 11. Electricallyinsulating regions 152 can be used as fillers so that the hot spotsoccur inside the caps. The electrically insulating regions 152 can beformed from an insulating ceramic.

A semiconductive cap can be formed by combining a cap and insulatingregions into one structure. For example, each semiconductive cap caninclude a conductive silicon carbide based ceramic doped with anonconductive material in the insulating regions. Alternatively, eachsemiconductive cap can include a nonconductive aluminum nitride basedceramic doped with a conductive material in the semiconductive capregion. The nonconductive material or the conductive material can beused to tune portions of the cap to the desired conductivity. In certainembodiments, the semiconductive cap is formed from AlN that is dopedwith TiB2 in the resistive region.

For reasons of completeness, various aspects of the present method andapparatus are set out in the following numbered clauses:

Clause 1. An embodiment includes n applicator for RF energy deliveredthrough a skin surface, including a base; a first electrode connected tothe base and extending from the base toward a first location of the skinsurface; and a first semiconductive cap disposed on a first distal endof the first electrode, the first semiconductive cap configured tocontact the first location of the skin surface. The RF energy isdelivered from the first electrode through the first semiconductive capthrough the skin surface. The first semiconductive cap has an electricalconductivity matched or substantially matched to the skin's electricalconductivity.Clause 2. The first semiconductive cap has an electrical conductivityabout 0.1 to about 2 times that of the skin.Clause 3. The first semiconductive cap has an electrical conductivity ofabout 0.03 S/m to about 3.0 S/m and a thermal conductivity of about 5W/m·° C. to about 500 W/m·° C.Clause 4. The first semiconductor cap extends along the skin surfacebeyond the first electrode and the extension of the semiconductor capdecreases in thickness.Clause 5. The applicator further includes a second electrode connectedto the base and extending from the base toward a second location of theskin surface, the second electrode being laterally offset from the firstelectrode along the skin surface; and a second semiconductive capdisposed on a second distal end of the second electrode, the secondsemiconductive cap configured to contact the second location of the skinsurface. The RF energy is delivered from the first electrode and thesecond electrode through the first semiconductive cap and the secondsemiconductive cap, respectively, through the skin surface. The secondsemiconductive cap has an electrical conductivity of about 0.03 S/m toabout 0.3 S/m and a thermal conductivity of about 5 W/m·° C. to about500 W/m·° C.Clause 6. The applicator further includes a second electrode connectedto the base and extending from the base toward a second location of theskin surface, the second electrode being laterally offset from the firstelectrode along the skin surface; and a second semiconductive capdisposed on a second distal end of the second electrode, the secondsemiconductive cap configured to contact the second location of the skinsurface. The RF energy is delivered from the first electrode and thesecond electrode through the first semiconductive cap and the secondsemiconductive cap, respectively, through the skin surface. The secondsemiconductive cap has an electrical conductivity matched orsubstantially matched to the skin's electrical conductivity.Clause 7. Each semiconductive cap comprises a semiconductive ceramic.Each semiconductive cap comprises a conductive silicon carbide basedceramic doped with a nonconductive material. Each semiconductive capcomprises a nonconductive aluminum nitride based ceramic doped with aconductive material.Clause 8. The applicator further includes a waveguide disposed betweenthe first electrode and the second electrode to deliver opticalradiation and an electrically insulating region having a triangularvertical cross section disposed between a surface of the waveguide andone of the semiconductive caps. The in the first semiconductive capincludes a third surface forming an obtuse angle with the first surfaceso that the second surface is longer than the first surface, and thethird surface abuts a surface of the waveguide.Clause 9. A method of treating a skin surface with RF energy applies tothe skin surface a first semiconductive cap disposed on a first distalend of a first electrode; and delivers RF energy from the firstelectrode through the first semiconductive cap through the skin surface.The first semiconductive cap has an electrical conductivity matched orsubstantially matched to the skin's electrical conductivity. The firstsemiconductive cap has an electrical conductivity about 0.1 to about 2times that of the skin. The first semiconductive cap has an electricalconductivity of about 0.03 S/m to about 3.0 S/m and a thermalconductivity of about 5 W/m·° C. to about 500 W/m·° C.Clause 10. The method of clause 9 further applies to the skin surface asecond semiconductive cap disposed on a second distal end of a secondelectrode; and delivers RF energy from the first electrode and thesecond electrode through the first semiconductive cap and the secondsemiconductive cap, respectively, through the skin surface. The secondsemiconductive cap has an electrical conductivity of about 0.03 S/m toabout 3.0 S/m and a thermal conductivity of about 5 W/m·° C. to about500 W/m·° C. The first semiconductor cap extends along the skin surfacebeyond the first electrode. The extension of the semiconductor capdecreases in thickness.Clause 11. The method of clause 9 further applies to the skin surface asecond semiconductive cap disposed on a second distal end of a secondelectrode; and delivers RF energy from the first electrode and thesecond electrode through the first semiconductive cap and the secondsemiconductive cap, respectively, through the skin surface. The secondsemiconductive cap has an electrical conductivity matched orsubstantially matched to the skin's electrical conductivity. A waveguideis disposed between the first electrode and the second electrode todeliver optical radiation. An electrically insulating region having atriangular vertical cross section is disposed between a surface of thewaveguide and one of the semiconductive caps. The first semiconductivecap includes a third surface forming an obtuse angle with the firstsurface so that the second surface is longer than the first surface, andthe third surface abuts a surface of the waveguide.

While the apparatus and method have been particularly shown anddescribed with reference to specific illustrative embodiments, it shouldbe understood that various changes in form and detail may be madewithout departing from the spirit and scope of the invention.

What is claimed is:
 1. An applicator for RF energy delivered through askin surface, comprising: a base; a first electrode connected to theapplicator base and extending from the applicator base toward a firstlocation of the skin surface; and a first semiconductive cap disposed ona first distal end of the first electrode, the first semiconductive capconfigured to contact the first location of the skin surface; whereinthe applicator is constructed and arranged so that the RF energy isdelivered from the first electrode through the first semiconductive capthrough the skin surface; and wherein the first semiconductive cap hasan electrical conductivity matched or substantially matched to theskin's electrical conductivity.
 2. The applicator according to claim 1wherein the first semiconductive cap has an electrical conductivityabout 0.1 times that of the skin to about 2 times that of the skin. 3.The applicator according to claim 1 wherein the first semiconductive caphas an electrical conductivity of about 0.03 S/m to about 3.0 S/m and athermal conductivity of about 5 W/m·° C. to about 500 W/m·° C.
 4. Theapplicator according to claim 1 further comprising: a second electrodeconnected to the applicator base and extending from the applicator basetoward a second location of the skin surface, the second electrode beinglaterally offset from the first electrode along the skin surface; and asecond semiconductive cap disposed on a second distal end of the secondelectrode, the second semiconductive cap configured to contact thesecond location of the skin surface; wherein the RF energy is deliveredfrom the first electrode and the second electrode through the firstsemiconductive cap and the second semiconductive cap, respectively,through the skin surface; and wherein the second semiconductive cap hasan electrical conductivity of about 0.03 S/m to about 0.3 S/m and athermal conductivity of about 5 W/m·° C. to about 500 W/m·° C.
 5. Theapplicator according to claim 1 further comprising: a second electrodeconnected to the applicator base and extending from the applicator basetoward a second location of the skin surface, the second electrode beinglaterally offset from the first electrode along the skin surface; and asecond semiconductive cap disposed on a second distal end of the secondelectrode, the second semiconductive cap configured to contact thesecond location of the skin surface; wherein the RF energy is deliveredfrom the first electrode and the second electrode through the firstsemiconductive cap and the second semiconductive cap, respectively,through the skin surface; and wherein the second semiconductive cap hasan electrical conductivity matched or substantially matched to theskin's electrical conductivity.
 6. The applicator according to claim 1wherein each semiconductive cap comprises a semiconductive ceramic. 7.The applicator according to claim 1 wherein each semiconductive capcomprises a conductive silicon carbide based ceramic doped with anonconductive material.
 8. The applicator according to claim 1 whereinthe semiconductor cap extends along the skin surface beyond theelectrode.
 9. The applicator according to claim 1 wherein the extensionof the semiconductor cap decreases in thickness.
 10. The apparatusaccording to claim 1 wherein the electrical conductivity ofsemiconductive cap substantially matched to skin conductivity reduceshot spot size.
 11. The applicator according to claim 7 furthercomprising a waveguide disposed between the first electrode and thesecond electrode to deliver optical radiation.
 12. The applicatoraccording to claim 1 wherein each semiconductive cap comprises anonconductive aluminum nitride based ceramic doped with a conductivematerial.
 13. The applicator according to claim 12 wherein thesemiconductive cap includes a third surface forming an obtuse angle withthe first surface so that the second surface is longer than the firstsurface, and the third surface abuts a surface of the waveguide.
 14. Theapplicator according to claim 1 wherein the semiconductive cap extendsalong the skin surface beyond the electrode edge and wherein the cap hasa trapezoidal vertical cross-section including a first surface, a secondsurface parallel or substantially parallel to the first surface, and athird surface forming an obtuse angle with the first surface, and afourth surface.
 15. The applicator according to claim 14, wherein thesecond surface is longer than the first surface and wherein the secondsurface is configured to contact the skin, and the first surface isconfigured to adjoin a respective electrode.
 16. The apparatus accordingto claim 14 wherein a triangular section of trapezoidal semiconductivecap maintains the hot spot inside the semiconductive cap and eliminatesthe hot spot at the junction of the cap with the skin.